The present invention relates to a lift and carry transfer apparatus and, more particularly, to a lift and carry apparatus that converts rotational movement of a crank member into harmonic linear motion for lowering and lifting an article transport carriage in conjunction with a carry device for moving the carriage between workstations.
Multiple station lift and carry transfer devices are generally known. Such devices either raise or lower an article or workpiece to an area where additional work is conducted on the workpiece and then transferred to a distant station for further processing. U.S. Pat. Nos. 2,804,962; 4,394,897; and 5,177,862 disclose such known configurations.
Prior devices suffer from inefficiencies in the type of vertical movement required of the platform or apparatus supporting the workpiece. When such prior devices move to or from a rest position, either raised or lowered, the article transfer apparatus must move slowly and cautiously when approaching and exiting the raised and lowered rest positions. Typically, the weight and load of the article and transfer apparatus does not allow for quick maneuvering, especially when the article transfer apparatus must be accurately aligned with corresponding industrial processing equipment. Any movement of the article transfer apparatus occurring between and beyond the stationary rest position should occur as rapidly as possible in order to reduce cycle times and increase the efficiency of the process.
This type of desired motion, i.e. having a slow start and finish with rapid movement there between, can be provided with harmonic motion. Harmonic motion may be described as having a sinusoidal velocity pattern wherein the object starts at a rest position and gradually accelerates to a maximum speed or velocity over a medial portion of the travel distance. Once the object is beyond the medial portion of the travel distance, the object begins to gradually decelerate until the object reaches a stationary position at the end of the travel. The described motion is typically provided by a hydraulic drive or pneumatic drive using a xe2x80x9cbleed and feedxe2x80x9d type system. These systems are generally complex in design and expensive to maintain thus affecting the efficiency of the apparatus and its associated processes.
Due to the complexity and limits of the lifting and lowering mechanisms of the prior devices, such devices are unable to adapt or vary the position of the workpiece in its lowered position. Prior devices require the workers, robots or other machines, at each individual workstation to be positioned to accommodate the lowered or raised position of the apparatus.
It is further well known in the art to employ conveyor-type mechanisms to transfer or index a workpiece down an assembly line from a first workstation to a second workstation for further manufacturing operations. Prior inventions have included individual drive mechanisms for each article transport platform and single drive mechanisms for moving multiple platforms. For example, U.S. Pat. Nos. 2,804,922; 4,394,897; and 5,177,862 disclose such systems. Prior devices also suffer disadvantages in efficiency and cost due to the complexity of the drive mechanisms. Electrical conductor drive mechanisms, for example, are disclosed in U.S. Pat. No. 5,177,862; or cam linkage drive mechanisms, for example are disclosed in, U.S. Pat. Nos. 2,804,962 and 4,394,897. These drive systems further suffer from shut down of the entire transfer system if the unit powering the drive between stations fails.
Prior art devices similarly have difficulty in converting from the traditional horizontal indexing to the lifting and lowering operation and vice versa. Prior designs require several mechanical operations to disengage the platform from the horizontal drive mechanism to allow engagement of the lifting and lowering mechanism to prevent dropping the article platform. For example, U.S. Pat. No. 5,177,862 discloses several mechanical steps for this operation. These additional operations reduce the cycle time, increase the complexity of the design, and add cost.
Thus, it would be desirable to provide a lift and carry apparatus that is simplistic in design and that will function in the lifting and lowering cycle and in the transferring of an article from a first station to a second station. It is further desirable to provide a lift and carry apparatus where the lifting and lowering mechanism employs harmonic linear motion that can easily be customized to vary the raised or lowered position of each station. It is further desirable to provide a lift and carry apparatus having an auxiliary drive mechanism to carry articles which can be engaged to maintain operations and increase efficiency. It is also desirable to provide a lift and carry apparatus with increased efficiency, lower initial cost and lower maintenance cost.
The present invention provides at least one article transfer carriage for lifting and lowering an article between a first position and a second position along a first path of travel and carrying the article between a first position and a second position along a transverse second path of travel. The apparatus provides at least one first drive connected to a frame for converting rotational movement of the drive to harmonic linear motion of the carriage along the first path of travel. The second drive is connected to the frame for moving the carriage back and forth along the transverse second path of travel.
The first drive includes a motor to rotate a rotary crank member and a follower attached thereto in discrete, 180xc2x0 semi-circular rotations defining a 0xc2x0 position corresponding to the first position and 180xc2x0 position corresponding to said second position along said first path of travel.
The second drive includes a motor attached to the frame and cooperatively engages a belt connected to the carriage for moving the carriage along the second path of travel.
The apparatus frame includes an elongate rail substantially parallel to the second path of travel and a lower rail portion attached to the elongate rail extending between the first and second positions along the second path of travel and discontinues just prior to the first and second positions along the second path of travel.
The carriage includes an open ended elongate follower guide that cooperatively engages the first drive follower for supporting and moving the carriage along the first path of travel while the carriage is positioned at the first or second position along the second path of travel.
The carriage further includes a lower guide. When the second drive moves the carriage away from the first and second positions along the second path of travel, the lower guide engages the lower rail portion supporting the carriage along the second path of travel. Once the carriage is supported by the lower rail portion, the first drive follower disengages the elongate follower guide and the first drive no longer supports the carriage along the second path of travel. When the carriage is proximate to the second position along the second path of travel, the elongate follower guide engages another first drive having the rotary crank member positioned at 0xc2x0 and the lower guide disengages the lower rail portion and the carriage is supported by the first drive. The carriage is moved from the first position to the second position and back again along the first path of travel by the first drive and once completed, the second drive moves the carriage from the second position back to the first position along the second path of travel to complete a cycle.
Where two or more carriages are used, the first drive synchronously moves the carriages between the first and second positions along the first path of travel and the second drive synchronously moves the carriages between the first position and the second position along the second path of travel.
Other objects, advantages and applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings.